Shrinkproof paper and method of manufacture, and laminated product



March 30, 1943. N w m 2,315,128

SHRINKE'ROOF PAPER AND METHOD OF MANUFACTURE, AND LAMINATED PRODUCTFiled Nov. 27, 1939 INVENTOR V va-1K5 Newkvk' ATTORNEY [CO(NCH2)2], thatis,

atented 30, 1943 SHRINKPROOF PAPER 3:

UFACTURE, LAATED PROD- UCT METHQD F Francis F. Newkirk, Attleboro, Massassighor to erican Reenio'rced Paper Company, Atticboro, Mass, acorporation of Massachusetts Application November 27, 1939, Serial No.306,304

18 Claims.

.in situations where it is subject to frequent wetting and drying. Forexample, when kraft paper is used for building purposes it will shrinkupon exposure to changing weather conditions so as to cause it to tearaway from its securin nails or to split. Kraft paper may shrink as muchas 4% or over crosswise of the sheet and somwhat less in the machinedirection whenit is alternately wetted and dried 7 times, which may betaken as representative of exposure to normal changes in weatherconditions during a period of 3 summer months.

It is the object of. my invention to treat paper, as for example kraftpaper, in such a way that without materially detracting from itsqualities of tearing and folding strength and flexibility it will berendered shrinkprooi to such a degree that its residual capacity toshrink crosswise in such a 7 cycle test is about 1% or preferably aslittle as So far as I am aware, paper such as kraft paper has never beenproduced with such a low residual shrinkage capacity prior to myinvention.

In my treatment I preferably employ urea ECOINHg) a] or thiourea andformaldehyde [HCI-IO] in an aqueous solution which is weakly acidifiedby a material such as ammonium thiccyanate [NEiCNS]. -As will bedescribed, I treat formaldehyde, that is, equal parts of urea andformaldehyde by weight when heated will be converted into aurea-formaldehyde resin 1100mm) i+znnciio=icomcmmn+znmo and ithasheretofore been suggested to treat In my process, on the contrary, Iemploy a bath which contains a substantial deficiency of urea ascompared with that which would be required according to the foregoingreaction to form the resin. I use less than one-half, although greaterthan one-fourth, as much urea as formaldehyde and preferably as littleas about one-third as much or slightly over,i. e. between limits of 1:3and 3:7. With the urea. and formaldehyde 1 make an aqueous solution thatis very dilute,.

employing preferably around thirty times as much water as urea. Thepercentage by weight of urea to water should be below 5% and above 2%,preferably between 3% and 4% and in the example given below isapproximately 3.4%. This bath is acidified within a pH range ofapproximately 2 to 4.5 using a weak acidifler preferably chosen from thefollowing group:

Ammonium thiocyanate Ammonium chloride Mon-ammonium phosphateIii-ammonium phosphate Tri-ammonium phosphate Ammonium bromide Formicacid My preferred formula for the bath is as follows, in parts byweight:

Where sized papers are to be treated, I would add to the above bath asmall amount of wettin agent, such as .25 parts by weight of a 10%solution of aerosol" (comprising an ester of sulfonated bicarboxylicacid) in water.

Kraft paper to be treated is wetted with the above bath as by immersiontherein for a brief interval of two or three seconds, and I then remove,as by doctoring, a large quantity of the bath that has been taken up.The damp paper should be less than 75% and is preferably from 30% to 50%heavier than the dry paper.

I then heat the paper to a temperature of from apprcxirriately 250 F. to300 F. (or higher but I without slngeing the paper) for a brief intervalsuch as one-half minute or less, by passing the paper through a hot airdryer. The paper is then ready for use and it has increased in weightless than 10% and usually about 5% to 7%, al-

though I have been able to reduce the shrinkage in paper with anextremely limited increase in weight such, for example as only 0.5%.

In the drawing I have illustrated diagrammatically apparatus which Ihave used effectively for my purpose. At 2 is indicated a tank inwetting agent, such asaerosol, is' employed. I,

may store it with the formaldehyde. At 6 and 8 are pumps for deliveringthe solutions in tanks 2 and 4 respectively through pipes .IO and I!respectively past the flow meters [4 and into mixing tank IS. The mixedsolution is drawn by pump i8 from tank l6 and is forced through line 20to trough 24 containing application roller 26 and through line 28 tospray pipe 30. The paper to be treated, supplied in a roll 32, is guidedover rolls 34 and 36,.over application roll 26, around guide roll 40 toconveyer belt 42 and into a dryer 48. The dryer illustrated has threesections designated 50,- 52v and 54, suitably partitioned and into whichhot air from a supply pipe 56 is blown through the ducts 58, 60 and 62-respectively. An exhaust in the-central compartment 52 suffices as Ihave indicated at. The dryer illustrated is approximately 150 feet longover all and the paper is conveyed through the dryer by a conveyer-beltl advancing the paper at 400 feet a minute or thereabouts. Thetemperature in the three. compartments may be uniform and within theapproximate temperature limits above noted, but in the specificapparatus illustrated the temperature in practice has been approximately250 F. in compartment 50, 280 F. in compartment 52 and 260 F. incompartment 54.

After the paper has been thoroughly wetted on both sides by passagebetween the application roll 26 and spray pipe 30, the excess solution,particularly on the surfaces, is removed by a rubber doctor blade and anair doctor 12. The paper passes thence through the dryer and as itemerges it is wound up at 80 by engagement with a surface windingr'oller 82. The rolls 84 are idle rolls and serve to tension the paperfor a tightly wound roll at 80.

The paper thus produced is substantially unimpaired in its originalqualities of flexibility, han- I composite reenforced sheets made byuniting two layers of kraft with interposed asphalt adhesive in whichare embedded reenforcing filaments such as unspun sisal fibers, stringsor the like, which composite sheets heretofore have had exception-v allyhigh shrinkages, such as 8% in the crosswise direction.

Although I have made extensive and careful experiments, I have as yetbeen unable to determine precisely the reactions which take placebetween the chemicals of the bath or between them and the cellulose ofthe paper, or the relative effects of those materials. My product,however, clearly lacks the characteristics of a paper or pulp that hasbeen treated with urea and formaldehyde in the conventional resinforming proportions. The products of such methods vary in theircharacteristics with the quantity of resin present from a hard resinloaded slabthat is water impervious to a lightly impregnated sheet thatis brittle and weak in tearing and folding strength and has a residualcapacity to shink which is as great, if not greater than that ofuntreated paper.

The treatments embodying my invention may be performed at low cost dueto the brief time interval required in the heating operation and therebymy invention doe not add materially to the cost of paper whose cheapnesscommends it for mostcommercial uses.

The word urea" when used in the specification and claims is intended toinclude thiourea in molecularly equivalent proportions.

This application is a continuation in part of my prior application Ser.No. 135,261, filed April 6, 1967.

I claim:

1. A sheet of paper rendered substantially shrinkproof by impregnationwith the product of the reaction within its structure of formaldehydeand an amount of urea which is substantially less than equal parts byweight with the formaldehyde, the said paper being at least 0.5% and nomore th.n 10% heavier than the same paper without said'impregnation.

2. A sheet of paper rendered substantially shrinkproof by impregnationwith the product of the reaction within its structure of anacidifiedbath of formaldehyde and an amount of urea which is by weightless than approximately one-half and more than approximately onefourththat of the formaldehyde, the said paper being at least 0.5% and no morethan 10% heavier than the same paper without said impregnation.

3. A sheet of paper rendered substantially shrinkproof by impregnationwith the product of the reaction within its structure of a weaklyacidifled bath of formaldehyde and an amount of urea which by weight isin proportion to the formaldehyde of from 3:7 to 1:3, the said paperbeing from approximately 5% to 7% heavier than the same paper withoutsaid impregnation.

' 4. A sheet of kraft paper impregnated with the product of the reactionwithin its structure of formaldehyde and an amount of urea which is byweight less than approximately one-half and more than approximatelyone-fourth that of the formaldehyde, the said paper being at least 0.5%and no more than 10% heavier than the same paper without saidimpregnation and being capable of a shrinkage of not more than 1% in itscross direction when alternately wetted and dried seven times.

5. A composite reenforced sheet of paper composed of two superposedsheets of the paper defined in claim 4 united by interposed asphalt 1.1which reenforcing strands are embedded, said composite sheet having avery inhibited capacity to shrink when repeatedly wetted and dried.

6. A composite reenforced sheet of paper formed of a plurality ofsuperposed plies of the paper defined in claim 4 and united byinterposed adhesive, said composite sheet having a very inhibitedcapacity to shrink when repeatedly wetted and dried.

'7."The'method of reducing the shrinkage in paper when repeatedly wettedand dried which consists in wetting the paper to substantially below itssaturation point with a dilute aqueous bath of urea and formaldehydecontaining by low' its saturation point with a. bath of formaldehyde andurea containing by weight less than approximately one-half and more thanapproximately-one-i'ourth as much urea as formaldehyde and about 30times as much water as urea, and

heating the damp paper so that its dry weight is increased at least 0.5%and no more than 10%.

'9. The method of reducing the shrinkage of paper when repeatedly wettedand dried which consists in wetting the paper to substantially below itssaturation point with a dilute aqueous bath of urea and formaldehydecontaining by weight less than approximately one-half and more thanapproximately one-fourth as much urea as formaldehyde and acidified by aweakly less than approximately one-half and more thanapproximatehrone-fourth as much urea. as formaldehydesaid bath beingacidified to a pH of between 2 and 4.5 by an acidifier chosen from thegroup consisting of ammonium thiocyanate, ammonium chloride,mon-ammonium phosphate, diammonium phosphate, trieammonium phosphate,ammoniumbromide and formic acid, and heat- I ing the damp paper to above200 F. for a brief interval to reduce its shrinkage while increasing itsweight at least 0.5% and no more than 10%. p

11. The method of reducing the shrinkage of T paper when repeatedlywetted and dried which consists in applying to the paper a dilute,aqueous bath, in an amount between and 50% of the dry weight of thepaper, containing urea and formaldehyde in the proportions of from 3:7to 1:3 by weight, and between approximately 3% and 4% urea by weight towater. said bath being acidified to a pH of between 2 and 4.5 with aweakly acidic material, and heating the damp paper.

12. The method of reducing the shrinkage in paper when repeatedly wettedand dried which consists in wetting the paper with an amount of bathapproximating 30% to 50% of the dry weight of the paper containing byweight approximately 22 parts of 40% formaldehyde, 3 parts urea, 2 partsammonium thiocyanate and '75 parts water, and heating the damp paper toa temperature of from 250 F. to 300 F. for approximately one halfminute. v 13. The method of reducing the shrinkage in paper whenrepeatedly wetted and dried which consists in applying to the paper anaqueous bath of formaldehyde and urea containing approximately one-thirdas much urea by weight as formaldehyde and sufficient water so that thepercentage by weight of urea to water is below 5% and above 2%, treatingthe paper to remove a large portion of the bath which it has absorbedand then heating the damp paper to an elevated temperature suiiicient tocause the materials absorbedby it from the bath to react.

14. The method of reducing the shrinkage of.

paper when repeatedly wetted and dried which consists in wetting thepaper to substantially below its saturation point with a dilute aqueousbath of urea and formaldehyde containing by weight less thanapproximately one-half and more than approximately one-fourth asmuchurea as formaldehyde, and heating the paper to from 250 F. to 300 F. forno more than a few minutes so that the dry weight of the paper isincreased-at least 0.5% and .no more than 10% and so that its shrinkageis reduced without sub stantially impairing its normal flexibility,handle,

hygroscopicity and folding and tearing strength. 15. A sheet of paperrendered substantially shrinkproof by impregnation with the product oithe reaction within its structure of iorineldehyde and an amount of ureawhich is by weight less than approximately one-half and more than approximately one-fourth that of the formaldehyde, the said paper being atleast 0.5% and no more than 10% heavier than the same paper without saidimpregnation.

. 16. The method of reducing the shrinkage in paper when repeatedlywetted and dried which includes applying to the paper a dilute bath ofurea and formaldehyde containing by weight less than approximatelyone-halr and more than ap-- proximately one-fourth as much urea asformaldehyde and subsequently heating the paper to an elevatedtemperature sufficient to cause the materials taken by it from the bathto react so that the dry weight of the paper is increased at least 0.5%and no more than 10%.

17. The method of reducing the shrinkage in paper when repeatedly wettedand dried which includes applying to the paper a dilute'aqueous bath ofurea and formaldehyde containing by weight less than approximatelyone-half and more than approximately one-fourth as much urea asformaldehyde, the said bath containing a material adapted to impartacidity of a pH of between 2 and 4.5 and heating the paper to cause thematerials taken by it from the bath to react so that the dry weight ofthe paper is increased at least 0.5% and no more than 10% and so thatits shrinkage is reduced without substantially im pairing its normalflexibility, handle, hygroscopicity and folding and tearing strength.

18. A multiply paper having a substantially reduced ability to shrinkwhen alternately wetted and dried which comprises two sheets of paperunited by asphalt in which reeniorcing strands are embedded, each ofsaid sheets having its ability to shrink reduced by impregnation withthe product of the reaction within its structure of a weakly acidifiedbath of formaldehyde and an amount of urea which is by weight less thana proximately V, and more than approximately that of the formaldehyde,each of said sheets being at least 0.5% and no more than 10% heavierthan the same paper without said impregnation.

. FRANCIS F. NEWKJRK.

